Conventionally, abrasion resistance has been considered to be important for heavy duty tires used for trucks, buses, and the like. Meanwhile, in heavy-truck transportation in Japan nowadays, the conditions in which tires are used are becoming less severe because of regulations of overloading, highway expansion, speed limit on highways, vehicle speed management using digital tachometers, and the like. Thus, greater importance is now also placed on the abrasion resistance under low severity abrasion conditions (conditions in which slip between tires and the road surface is less likely to occur, such as running at a constant speed on highways).
With respect to the abrasion resistance under low severity abrasion conditions, adhesive wear greatly contributes to the abrasion. Thus, it is considered to be advantageous to use natural rubber or styrene butadiene rubber rather than butadiene rubber. However, since tires are also, as a matter of course, required to have abrasion resistance under high severity abrasion conditions (conditions in which slip between tires and the road surface frequently occurs when starting or braking), for example, it is necessary to combine butadiene rubber. Thus, it is difficult to improve abrasion resistance under both of the conditions in a balanced manner. Furthermore, energy saving by reducing heat build-up of tires, improvement of chipping resistance, and the like are also demanded. Therefore, it is also difficult to improve these properties at the same time.
Patent Literature 1 discloses a technique of mixing a specific carbon black with butadiene rubber to enhance abrasion resistance while maintaining low heat build-up properties as well as fatigue resistance. However, the technique cannot sufficiently improve some properties such as abrasion resistance under low severity abrasion conditions. Patent Literature 2 discloses a technique of mixing a specific carbon black to enhance chipping resistance and abrasion resistance while maintaining low heat build-up properties. The technique, however, still has room for improvement in terms of low heat build-up properties and the like.